Heating controlling system in a multizone type continuously heating furnace

ABSTRACT

A heating controlling system in a multizone-type continuously heating furnace having a preheating zone, heating zone and soaking zone in sequence for obtaining an object heated in the furnace which may be extracted from the soaking zone at any objected temperature by determining the temperature of the heated object at the inlet of the heated zone from the atmospheric temperature in the preheating zone and other factors, controlling quantity of fed heat in the heating zone from said temperature and then adjusting quantity of fed heat or moving velocity of the heated object in the soaking zone.

[50] Field of 263/6. 52

[56] References Cited UNITED STATES PATENTS 2,620,l74 12/1952Passafaro..................... 263/6 3,252,693 5/1966 Nelson 263/3Primary Examiner-John J. Camby Anomey-Wenderoth, Lind & Ponack ABSTRACT:A heating controlling system in a multizone-type continuously heatingfurnace having a preheating zone, heating zone and soaking zone insequence for obtaining an object heated in the furnace which may beextracted from the soaking zone at any objected temperature bydetermining the temperature of the heated object at the inlet of theheated zone from the atmospheric temperature in the preheating zone and263/52 other factors, controlling quantity of fed heat in the heating263/6 zone from said temperature and'then adjusting quantity of fed F27)9/40 heat or moving velocity of the heated object in the soaking :zone.

Hiroshi Matuno; Toshlya Morisue, both of Kltakyushu, Japan Appl. No.798,729

Feb. 12, 1969 Dec. 14, 1971 Yawata Iron 8; Steel Co., Ltd. Tokyo, JapanFeb. 15, 1968 Japan 43/9540 MULTIZONE TYPE CONTINUOUSLY HEATING FURNACE1 Claim, 7 Drawing United States Patent [72] Inventors [22] Filed [45]Patented [73] Assignee [32] Priority [54] HEATING CONTROLLING SYSTEM INA I a wmawazwe :52

20.82% 53 EEEE 93w Ill.

. wz Ckmm me. 41 masmk wzrEmI SOAKING ZONE 4 HEATING TEMPERATURE 9 G(DIMENSION 7 Eu zoCouGa 535E825 93m $520255 2555 m 20 5 12 85mm 9 30 5GB HEATING ZONE: 2 HEATING TEMPERATURE DIMENSION PHYSICAL CONSTANT PSPHYSICAL CONSTANT PS PATENIEU DEC I 4 IIIII SHEET 1 BF 6 FIG. I I

FIG. III) FIG. 2

I I E $35825 HEATING I TEMPERATURE 9 G 3 3 9 SOAKING zoNE.4 emo wZCLum304m Juan.

wzrrmw wank HEATING ZONE: 2

TEMPERATURE GmI T HEATING DIM E N s I ON PHYSICAL CONSTANT P DIM E N SION PHYSICAL CONSTANT P5 INVENTOR Ma funo Hiras/n' Tosh/ya Mar/suewmzfilIoiLlikii uwdi ATTORNEY PATENIEU 115m 412m sum 2. HF 6 mohamiouINVENTOR S at/m0 H l'roshi M or/sue ATTORNEY SHEET 6 OF 6 UPPER J PARTLOWER PART FIRST SECOND THIRD FOURTH FIFTH HEATING HEATING HEATINGHEATING TI zoNE z oNE zoNE zoNE zoNE UPPER i ART Gs s STEEL I MATERIAL Mt'c t CQ 0 ti ti+d i L E 'NLET OUTLET LOWER t'GB \dQiB PART INVENTORSHIRosHI MATUNO TosHIYA MORISUE BY fi 'y z ATTORNEYS BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to acontinuously heating furnace and more particularly to a system forcontrolling the temperature of continuously heated steel materials to atemperature best adapted to a hot-rolling thereof.

2. Description of the Prior Art Generally, in the temperature control ofa continuously heating furnace it is requisite that metal be uniformlyheated to a temperature adapted to a rolling thereof and be able to besupplied corresponding to the rolling velocity required in the rolling.For this purpose, in a continuously heating furnace there has beenadopted an automatic combustion controlling system, which is, however,to control the atmospheric temperature within the furnace, but is not tocontrol the temperature itself of the object being heated. Consequently,by this known control system it is so difficult to control the operationof the heating furnace in response to the frequently varying dimensionof the object to be heated, the variation of the kinds of objects andthe fluctuation of the extracting velocity that at present only a fixedpattern control or an indirect control disregarding these variations iscarried out and the significance of the automatic control in the truesense of the words is almost extinguished.

Therefore, the accurate control of the temperature within the heatingfurnace in response to such various variations of the object to beheated as mentioned above was to depend on the high degree of skill,very great efforts and carefulness of the heating furnace operators.That is to say, today the control of the temperature of the heatedobject in the furnace operation is made mostly by controlling theatmospheric temperature of each zone by measuring the surfacetemperature of the heated object by optical means. However, in suchcase, there exists no standard of judgement and the control is resort toexperiences and intuition obtained for a number of years. Further, evenin the case of a control by utilizing feedback information, there arevarious disadvantages, that there exists a time lag between the time ofobtaining an information and the operation, because the operator canfirst obtain the information, when the operation proceeds already tosequent steps, that is, a crude rolling and finishing rolling, that theinformations are not uniform in the state of defonnation and furtherthat the steel material (heated object), on which information has beenobtained, and the steel material (heated object) to be compensated onthe basis of this information are not always of the samecharacteristics,which makes the compensation difficult.

Further, as regards the temperature of the heated object in athree-zone-type continuously heating furnace it is to note in generalthat, as the temperature of the heated object in the preheating zone isrepresented only as a function of the time required for the passage ofthe heated object and the residual temperature and the amount of theexhaust gas discharged out of the heating zone, that is, the quantity ofthe sensible heat of the exhaust gas, it is generally almost impossibleto control the heating of the heated material and further, as the heatedobject does not come to be red hot, it is difficult to measure thetemperature of the heated object even at the end of the preheating zone.However, in order to accurately control the heating in the heating zoneso as to heat the object to a temperature adapted to a hot-workingthereof, it is indispensable to accurately measure the temperature ofthe heated object at the end of the preheating zone, that is, at theinlet of the heating zone, which was, however, impossible according toany known method.

SUMMARY OF THE INVENTION In view of such actual circumstances asabove-mentioned the present invention has for its object the control ofcombustion in each zone as in an independent state by determining theinlet temperature of the heated object in each zone, taking also themoving velocity, physical constant and dimension of the heated materialsinto consideration so that any desired rolling temperature of the heatedobject may be finally obtained.

Another object of the present invention is to carry out an economicaloperation by reducing personnel and saving fuel consumption byefficiently and automatically operating a continuously heating furnaceso that the heated object may be extracted out of the heating furnace atany desired temperature. That is, the present invention is to provide aheating controlling system in a multizone-type continuously heatingfurnace, in which furnace a preheating zone, heating zone and soakingzone being formed in sequence, characterized by determining bycalculation the temperature of a heated object at the inlet of theheating zone according to a relative formula of a predeterminedtemperature of the heated object from the controlled or uncontrolledatmospheric temperature in the preheating zone and the dimension, movingvelocity and physical constant of the heated object, controlling thequantity of fed heat in the heating zone from the said determinedtemperature, the dimension, moving velocity and physical constant of theheated object and a predetermined rolling temperature and furtheradjusting the quantity of the fed heat or the moving velocity of theheated zone in the soaking zone from the difference between theabove-mentioned predetermined rolling temperature and soaking zone inlettemperature and the dimension and physical constant of the heated zone.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 3 is a graph comparing the setvalues according to the 7 present invention and set values in actualoperation.

FIGS. 4(a) and (b) show fuel (heavy oil) flow volumes (amounts of feed)in a continuously heating furnace controlled by the system of thepresent invention and in a continuously heating furnace not using thesystem of the present invention, in which (a) shows the former and (b)the latter.

FIG. 5 is a graph showing the measured temperatures of the heated object(slab) at the soaking zone outlet in the case of the control by thesystem of the present invention.

FIG. 6 shows a simplified model of a continuously heating furnace.

FIG. 7 shows a heat balance model of a heated object in any heating zoneaccording to FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention shall nowbe explained with reference to an embodiment in the following. First,the contents of the present invention shall be explained with referenceto a threezone-type heating furnace for example.

In FIG. 1 in which is a schematic view of a three-zone-type continuouslyheating furnace, l is a preheating zone, 2 and 3 are respectively anupper heating zone and lower heating zone, 4 is a soaking zone and 5 isa part of objects to be heated. Further, in FIG. 2, 6 is an outlet ofthe heating zone and 8 is an inlet of the same. 7 is an inlet of thesoaking zone and 13 is an outlet of the same. 9 is a heating zone fuelinflow volume. 10 is a combustion air volume. 11 is a heating furnaceset temperature. 12 is a thermometer.

The temperature of the heated object at the end of the preheating zone 1can be represented by the following formula as a function of thequantity of sensible heat of the exhaust gas from the heating zone andthe time of the passage of the heated object through the preheatingzone:

wherein time is a mean temperature of the heated object at the outlet ofthe preheating zone,

is an atmospheric temperature in the preheating zone,

6 is a volume of flow of the exhaust gas,

V is a moving velocity of the heated object,

P is a physical constant of the heated object,

D is a dimension of the heated object and C is a specific heat of theexhaust gas.

Therefore, the temperature at the end of the preheating zone, that is,at the inlet of the heating zone can be determined 10 by calculation bythe above-mentioned formula from the physical constant and dimension ofthe heated object given in advance by detecting the atmospherictemperature in the preheating zone and the moving velocity of the heatedobject. One of the features of the present invention is to determine thetemperature at the preheating zone outlet of the heated object.

The thus determined average temperature at the preheating zone outlet ofthe heated object is then used for the base of the heating control ofthe heating zone.

The heating of the object is mostly carried out in the upper heatingpart and lower heating part with the heated object path in the heatingzone as a boundary between both parts. The control of the heating zoneand soaking zone shall be described with reference to FIG. 2 in thefollowing.

The control of the heating in the heating zone 2 is mostly carried outwith the heating temperature, independently of the control of thesoaking zone 4 following the heating zone 2. First of all, thetemperature of the heated object at the outlet of the heating zone 2, hthat is, at the inlet 7 of the soaking zone is so set as to coincidewith the temperature required for the hot-working in the subsequentstep. The temperature of the heated object 5 in the heating zone 2 iscontrolled by controlling the heating temperature as mentioned above.The temperature 0 mo of the heated object at the above-mentioned heatingzone outlet 6 is represented by the following formula as a function ofthe heatingzone heating temperature 0 heated object moving velocity Vheated object temperature 67ml at the heating zone inlet 8, heatedobject dimension D and physical constant P of the heated object:

l( 6s! s; 0771i, s, s) Therefore, when V 0mi,D and P are given, theoptimum atmospheric temperature for passing the heated object 5 throughthe heating zone outlet 6 at an objective temperature, that is, theheating furnace set temperature 11 can be determined by the formula fi=r,' omo, V amt, P P when the atmospheric temperature is determined, thefuel inflow volume 9 and combustion air volume 10 can be readilydetermined. Therefore, if the combustion is controlled by using thesevalues as set values, the temperature of the heated object in theheating zone can be made the optimum temperature.

If the control of the heating in the heating zone is properlyaccomplished, the actual temperature m0 of the object thus heated in theheating zone and the temperature m!" of the soaking zone inlet 7 shouldbe ideally equal to each other. However, the temperature of the heatedobject leaving the heating zone is measured with the thermometer 12 inanticipation of the case that, due to any external disturbance, theactual temperature Hmo of the heated object 5 might not reach thepredetermined temperature at the soaking zone inlet.

in such case, when the temperature of the heated object 5 deviates fromthe predetermined temperature, there must be made a necessary heatingcorrection as is described later, in order to obtain the objectivetemperature at the soaking zone outlet. However, in case the heatingzone outlet temperature is the predetermined temperature, heat is fedfor soaking.

That is to say, the control of the heating or soaking in the soakingzone 4 is carried out by utilizing the following relative formula in thesame manner as in the heat control in the heating zone:

5m is an objective temperature for extracting the heated object,

0 is a heating temperature in the soaking zone,

Omi' is a temperature of the heated object at the soaking zone inlet,

P is a physical constant of the heated object and D is a dimension ofthe heated object.

From this relative formula, the moving velocity V of the heated objectfor extracting it at the object extracting temperature is determined ask V ,=F,(0 Omo', a t", D P Therefore, the temperature of the heatedobject at the outlet of the soaking zone is controlled by the movingvelocity on the basis of the relation of the above formula.

Further, in case the moving velocity of the heated object in the soakingzone, that is, the extracting velocity of the heated object is given byan external factor, for example, a rolling velocity in a roll, theobjective temperature of the heated object is controlled by adjustingthe soaking zone heating or soaking temperature,'asis determined by Theabove-mentioned is of the case of a three-zone type which has no burnerin the preheating zone and therefore in which the heated object cannotbe controlled in the preheating zone. However, generally, even in thecase of a multizone type having a burner, the independent furnace setheating temperature or moving velocity for the heated object to passthrough the outlet at the objective temperature can be determined byregarding the preheating zone, heating zone and soaking zonerespectively as independent furnaces and measuring or calculating thetemperature of the heated object at the inlet of the independent furnaceor from the above-mentioned formula model if the objective temperatureat the outlet is determined. Therefore, a temperature adapted to rollthe heated object can be obtained automatically and accurately bycarrying out the same operation for each independent furnace.

In the following the present invention shall be further explained indetail by giving a calculation example to concretely realize thereby thefundamental idea of the present invention, particularly with referenceto FIGS. 6 and 7.

In FIG. 6 there is shown a usual continuously heating furnace, theinterior of which is divided into five parts, that is, the first,second, third, fourth and fifth heating zones, seen from the inlet forcharge at the left end, each of which being regarded as an independentfurnace and being divided into an upper part and a lower partrespectively.

In the heating furnace of such a construction as above mentioned thefifth heating zone may be regarded as a soaking zone, and thetemperature in each upper part and lower part of the respective zonescan be controlled separately.

In view of a heat balance relating to a very small section of a heatedobject in a zone i.e., the i-zone, as shown in FIG. 7, while supposingthat the furnace temperatures in the upper and lower parts of respectiveheating zones of such a heating furnace as above mentioned are constantfor each part, the heat transmissions to the upper and lower parts insaid small section of the heated object in FIG. 7, dQ,, dQ are given bythe following formulas respectively:

QI I 'GS c) I Qs sK GB c) As the sum of the above formulas (dQ,=dQ,'+dQcomes to the quantity of heat to be given to the heated object, thefollowing equation can be obtained.

I JUG c)+ B ('GB c)] c+ c) 'c'1 wherein,

M: Treated amount of a heated object in the i-heating zone (kg/hr.)

Cf: Specific heat of a heated object in the i-heating zone (K- cal./KG.C.)

1': Length of heated objects in the i-heating zone (m) X: Distance of aheated object in the i-heating zone from the inlet thereof (m) H,=h +hn' m+ cn' wherein,

h h Radiation heat transfer coefficient of the upper and lower parts ofthe i-heating zone respectively (KcaL/m. hr. C.)

h,,', h Convection heat transfer coefficient of the upper and lowerparts of the i-heating zone respectively (KcaL/m. hr. C.)

Further, as a linear radiation heat transfer coefficient is introducedthe following formulas (5) results:

0-: 4.88(Stephan Boltzmann constant) 1,": Average temperature of aheated object in the i-heating zone C.)

wherein,

L,-: Furnace length of the i-heating zone (m) Then, the temperature of aheated object at the inlet of the iheating zone is supposed to be r,,'that is,

tc X=0=r,., (7) and further the relation between the furnace temperaturein the upper part and that in the lower part is supposed to be, as shownin the following formula (8):

GB GI ()t' is the temperature ratio between the upper part and lowerpart of the i-heating zone).

When a solution of the formula (3) is sought under these conditions asabove mentioned, there can be obtained the following equation:

From the formula (9) it is possible to calculate the furnacetemperatures of the upper and lower parts of the i-heating zone. 1 I atwhich temperatures the heated object which has passed through inlet ofthe i-heating zone with a temperature of t,,'( C.) may pass through theoutlet of the same zone with a temperature of t C.

If a quantity of heat Qf (KcaL/hr.) which is necessary for the heatedobject, is composed of a quantity of heat Q, (1(- cal./hr.) which flowsin from the upper surface and a quantity of heat Q (KcaL/hr.) whichflows in from the lower surface, Q=Q.+QB

On the other hand, Q}, Q, can be obtained by substituting the formula(9) and integrating the substituted over a range of 0 to L In thepreheating zone having no combustion equipment an average temperature ofa heated object is calculated according to the formula (9), while in theheating zone and soaking zone it is possible to calculate temperaturesset in the furnace or quantity of fed heat by utilizing the formulas l0)and l 1 On the other hand, if the maximum set temperature which isrealizable in the upper part of the heating zone is made t the maximumtreated amount of a heated object M corresponding to said maximum settemperature can be obtained by modifying the formula 10).

B'M(82%.... n )/(fiz bm sq)l Further, the shortest treating pitch in inthe i-heating zone P,,, which can afford said maximum heating capacityis calculated by the following formula l5 that is,

P 36OOl d L- Jam (1 wherein,

(l :Thickness of a. steel material (m), :l)ensity of a. heated object(kg/m3), fnlNumber of operating furnace, k

mzFirst value ofj which satisfies the relation of E i= (sum of widths ofu slab from an extracting port) ZL On the other hand, the time that aheated object stays in the soaking zone (fifth zone), T (minute), whichmay secure the minimum soaking degree and may eliminate skid marks tosuch a degree as would not impede a subsequent hot rolling, is obtainedby the analysis of heat transfer. That is,

LFT

wherein,

L Total length of Furnace.

Therefore, a treating pitch in the soaking zone P, is given by theformula l7).

60LF (d4:0) fn-W- T (m is the first value of k which satisfies therelation of an independent furnace and consequently the heat controllingis carried out for each zone separately, such set heating temperatureand moving velocity of a heated object in the zone can be determinedaccording to the above-mentioned formulas as the heated object may passthrough the outlet of the zone with an objective temperature to beobtained, if the temperature of the heated object at the inlet of thezone is measured or calculated and the objective temperature at theoutlet thereof is determined.

An actual operation example according to the system of the presentinvention shall be described in the following.

F IG. 3 shows the case of the operating a continuously heating furnaceby the system of the present invention. In the graph, shown with thesolid line are planned values by the system of the present invention andshown with the dotted line are corrected values (actual operationvalues) based on the differences between said planned values and actualvalues. As evident from this graph, a very accurate control can be made.

Further, FIG. 4 comparatively shows the amounts of fuel (heavy oil) fedto the upper heating zones in a continuously heating furnace controlledby the system of the present invention and in a continuously heatingfurnace not using the system of the present invention. As evident fromthis graph, in case the system of the present invention is used, a farmore precise control can be made and the fuel consumption can be madeefficient.

FIG. 5 shows the results of measuring the temperature of the heatedobject (slab) at the soaking zone outlet in the case that the system ofthe present invention was worked. It is found that said temperaturevaried depending on the thickness of the heated object but wassubstantially constant for the same thickness and that therefore thecontrol was made properly and accurately.

Thus, accordingly to the present invention, a continuously heatingfurnace can be operated automatically under optimum condition so thatthe heated object may be extracted at a fixed temperature, therefore theoperation can be carried out efficiently and its effect is very high.

What is claimed is:

l. A process for controlling the direct heating of a steel material in amultizone type continuously heating furnace, in which furnace apreheating zone, a heating zone and a soaking zone are formed insequence, comprising the steps of measuring the atmospheric temperaturein said preheating zone, determining the temperature of said heatedsteel material at an inlet of said heating zone from said measured valueof said atmospheric temperature in said preheating zone and thedimension, moving velocity and physical constant of said heated steelmaterial, controlling the fuel inflow volume and combustion air volumein said heating zone from said temperature, simultaneously adjusting thequantity of heat fed to or the moving velocity of said heated steelmaterial in said soaking zone from the difference between apredetermined rolling temperature and the measured value of thetemperature of said heated steel material at the inlet of said soakingzone and the dimension and physical constant of said heated steel.

